Overview page does not support namespace-scoped users

[jasonmadigan]

The Overview page was built with cluster-admin in mind. Namespace-scoped users will see incomplete or missing stuff - for example, the gateway health card watches gateways cluster-wide and will not show results for users without cluster-level read access. We need to revisit what the Overview page should show for namespace-scoped users.

We could add a picker, but that may subvert the point of the view as a general "overview" page. Needs some thought.